Cellulose derivative lacquer and sheeting coated therewith



Patented Oct. 10, 1944 CELLULOSE DERIVATIVE LACQUER AND SHEETIN G COATED THEREWITII Alfred L. Rummelsburg,

Wilmington, Del., assignor to Hercules Powder Company, Wilmington,

Del., a corporation of No Drawing. Original a 1940, Serial No. 372,49

Delaware pplication December 31,

0. Divided and this allplication March 10, 1942, Serial No. 434,043

Claims.

This invention relates to a transparent material and more particularly to a transparentwrapping sheet of regenerated cellulose, provided on one or both sides with a transparent coating composition.

Transparent wrapping sheets have heretofore been provided with surface films of cellulose derivative compositions such as compositions embodying cellulose nitrate. a resin and a plasticizer, and where moisture-proofness is desired, a wax or waxy material, the purpose of this coating being to enhance the utility of the wrapping sheet and to impart to it desired resistance to transmission of water either in liquid or in vapor form. In 'my copending application, Serial No. 343,166, filed June 29, 1940, there is disclosed the use of straight polymerized rosin having an acid number of less than about 140 and preferably ranging from about 100 to about 135, as the resinous component of such compositions, the use of such low acid number polymerized rosin having proved advantageous because it yields a film which is clear and haze-free even after the expiration of a long period oi time. However, it is difllcult and expensive to prepare polymerized rosin having an acid number within the range described in said application.

It is an object of the present invention to provide a transparent haze-free lacquer in which the resinous component embodies high acid number polymerized rosin. Another object is to provide a transparent base material coated with such a lac-' quer. Another object is to provide a transparent wrapping sheeting coated with such a lacquer. Another object is to provide a permanently hazefree transparent wrapping sheet. Another object is to provide a resin embodying high acid number polymerized rosin but freefrom the tendency to impart haze to a transparent cellulose derivative composition. Another object is to provide a process for making such a resinous material from high acid number polymerized rosin.

I have discovered that polymerized rosin having, when manufactured, an 'acid number above 140, the acid number of which has been reduced to between about 60 and about 125v by partial esterification with glycerine, displays freedom from haze-forming tendency when incorporated in a transparent cellulose derivative composition such s transparent lacquer for coating transnumbe parent wrapping sheets or the like. At the same time. this resinous material shows a sunicient moisture resistance. Polymerized rosin which has been substantially completely esterified with 5 glycerine, say to an acid number of 25 or lower,

while imparting good gloss and adhesion to the lacquer, does not possess adequate resistance to Since it is much easier and prepare high acid number water or moisture. more economical to 10 polymerized rosin and to partially esterify it to The present invention may be carried out by I esterifying polymerized rosin having an acid num-- ber above 140 and w ch would impart an objectionable haze to a transparent cellulose derivative lacquer, with from about 2% to about 5% by weight of glycerine based on the weight of polymerized rosin. For the substantially complete esterification of polymerized rosin, it is customary to employ 12% of its weight of glycerine. Therefore, it will be seen that the present invention involves the use of from about 17% to about 42% by weight of the glycerine normally used for substantially complete esterification. Complete reaction of high acid number polymerized rosin with 5% of its weight of glycerine gives an acid number of about 60. Complete esterification of high acid number polymerized rosin with 2% of its weight of glycerine gives an acid number of about 125. The resins prepared with quantities of glycerine materially on either side of this range do not show advantageous properties in transparent wrapping sheet lacquer. Thus, the use of less than 2% of glycerine results in the production of an objectionable haze in the coating. The use of more than 5% of glycerine re,

sults in the production of a film which has very poor moisture resistance.

The partial glycerine esters may be prepared by heating a mixture of polymerized rosin with the requisite amount of glycerine at a temperature of about 270 C. for a period of time sumcient to bring about action of the glycerine with the polymerized rosin. Normally, this period of time will be at least 3.5 hours. Preferably, the reaction is carried out under an air condenser, and in the presence of an inert atmosphere such as carbon dioxide, produced for example by bubbling inert gas through the reaction mixture. I

The lacquer in accordance with the present invention may comprise a cellulose derivative and the partial glycerine ester prepared as above, as its principal film-forming ingredients. However, the lacquer may in addition desirably embody substantial proportions of a wax or waxy material and a suitable plasticizer.

In order to form the lacquer, the film-forming ingredients which are relatively non-volatile are dissolved in a suitable quantity of a suitable volatile-organic solvent. The resulting lacquer is then applied to the transparent base as, for example, to one or both sides of a transparent wrapping sheet of regenerated cellulose in any suitable manner as, for example, by roll coating, spraying, brushing, flowing, etc., after which the wet film is dried to remove the volatile solvents and form the final product. If desired, the coated base may be subjected to an elevated temperature suillcient to melt the wax in the composition and simultaneously volatilize residual solvent.

As the transparent base to which the lacquer is applied, 1 may use any transparent base which is preferably insoluble in the usual lacquer solvents, such as glass, transparent regenerated cellulose articles such as regenerated cellulose sheeting, gelatin sheeting, casein sheeting, cellulose acetate sheeting, rubber hydrochloride sheeting, etc. However, the invention is particularly applicable to regenerated cellulose sheeting because such sheeting without lacquer coating is extremely lustreless and permeable to the transmission of water.

As the cellulose derivative, it is preferred to employ nitrocellulose of a grade which gives the desired viscosity in the resulting lacquer. Mixtures of several grades of nitrocellulose of this viscosity may be used if desired. I have found it particularly advantageous to employ nitrocellulose of one-half second viscosity. Instead of using nitrocellulose, other cellulose derivatives may less preferably be employed, such as ethyl cellulose, benzyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate and the like.

The range of cellulose derivatives may vary within quite wide limits, for example, from about 25% to about 60% by weight of total solids in the composition, between about 40% and about 50% lose.

If desired, the partially esterifled glycerine ester of polymerized rosin may be treated to remove traces of light ends, such as rosin oil and the like. These light ends are objectionable in that they cause the resin to impart an undesirable tackiness to the resulting film. These light ends may be removed from the ester by heating at reduced pressure, for example, at about 1 mm. pressure and 240-280 C. or higher, under which conditions oils and also unpolymerized rosin can be removed by distillation. Alternatively, the polymerized rosin before esteriflcation may be treated in this manner to remove rosin oils and unpolymerized rosin. The polymerized rosin which is esterifled may be polymerized in any of nitrocellusubstantially complete realthough it is preferred to employ;

suitable manner as, for example, by means of sulfuric acid, phosphoric acid, tetraphosphoric acid, hydrofluoric acid, boron trifiuoride, amphoteric meta1 halides, etc. The polymerized rosin may have been, or the partial glycerine ester thereof may be, further refined in any desired manner for example, by means of selective solvents such as furfural, etc.; selective adsorbents such as fullers earth, etc., to reduce its color to the desired figure. It may also have been heat treated at 250-325 C., desirably in an inert atmosphere, to bleach its color. If desired, the partial glycerine ester of polymerized rosin may be prepared by polymerizing the partial glycerine ester of rosin by any of the methods known to the art. Instead of employing rosin itself as the original starting material for the partial glycerine ester of polymerized rosin, I may use equivalent rosin acids such as abietic acid, pimaric acid, sapinic acid, etc. The original rosin may be refined or unrefined, heat treated, partially distilled, etc.

The amount of partial glycerine ester of acid number from 60 to used in the lacquer may vary within relatively wide limits as, for example, from about 20% to about 60% by weight of the total solids in the lacquer. Within this range, it is preferred to employ between about 30% and about 40% of weight of the partial ester. It has been found that the employment of the partial ester of polymerized rosin in the lacquer in these amounts produces a film which overcomes the disadvantages of prior art lacquers wherein the resinous component was rosin or ester gum. The partial ester of polymerized rosin is completely compatible withthe cellulose derivative, and with the wax or waxy material, both in the formulation of the lacquer and in the resulting dried coating.

It is preferred to employ a wax or wax-like material in the lacquer composition in order to impart moisture-proof properties to the wrapping sheet coated with the lacquer. In this specification, and in the claims appended hereto, I use the term wax to designate any suitable waxes such as true waxes, or paraflin wax, or equivalent wax or wax-like materials which have the property of imparting water-proofness to the lacquer. It is preferred to use parafiln wax of relatively high melting point (at least 55 C.) However, other waxes may be employed such as, for example, carnauba wax, spermaceti, wool wax, beeswax, Japan wax, Chinese insect wax, psylla wax, montan wax, palm, sugar cane wax, pisang wax, candellila, cottonseed wax, gondang wax, pimela wax, bayberry wax, etc. and similar waxy materials such as tallow, waxy chlorinated naphthylenes (Halowax), palmitic acid, stearic acid stearin, ceresin, ozokerite, synthetic waxes such as opal wax, petroleum jelly, etc. The amount of wax employed may vary between about 1% and about 20% by weight of total solids in the lacquer and preferably within the limits of between about 5% and about 10% by weight.

It is preferable to incorporate into the lacquer a plasticizer of suitabl type such as, for example, from about 5% to about 40% of one of the following plasticizers or mixtures thereof, having regard to the particular cellulose derivative present in the formulation: dibutyl phthalate, I

dimethyl phthalate, diethyl phthalate, diamyl phthalate. cyclohexyl phthalate, benzyl phthalate, dibutyl tartrate, diamyl tartrate, ethyl abletate, benzyl abietate, diacetin, triacetin. sucrose yl phathalyl ethyl glycollate, butyl phthalyl butyl glycollate, ethyl phthalyl ethyl glycollate, triphenyl phosphate, tricresyl phosphate, camphor, blown castor oil, etc.

Ifdesired,-a suitable dye or soluble dyestufl' may be incorporated in the lacquer provided it does not materially reduce the transparency of the lacquer or the film made therefrom.

The foregoing non-volatile constituents are dissolved in a suitable solvent therefor, it being preferred to employ mixtures of solvents, to form a lacquer of the desired consistency for application by the particular method .to be used. Any of the known lacquer solvents may be employed. Particularly satisfactory results have been obtained by using a mixture of butyl acetate, ethyl acetate, ethyl alcohol, butyl alcohol and toluene in various proportions. The principles, of formulating the lacquer solvent mixture are well understood to those skilled in the art, it being recognized that a solvent mixture should be employed which gives a suitable drying rate and which does not adversely affect the properties of the resulting solid film. It is particularly important to avoid condensation of moisture upon the lacquer film during evaporation of the solvents and to use solvents which do not cause blushing or clouding of the film as the solvents evaporate. As solvents, there may be employed any of the known ,lacquer solvents such as alcohyrocarbons, ethers, halogenated hydrocarbons, nitro paraflins, or mixtures of the foregoing solvents, etc. The concentration of non-volatile or film-forming ingredients in the lacquer will depend upon the consistency desired and may vary, for example, from to 50% and preferably from 20 to 25%. For ex ample, I have found taining.22% of total solids results in a composition of such consistency that it may be readily applied by the usual coating methods to form a hols, ketones, esters,

thin film which imparts the desired propertiesto the base.

In some cases, the composition may be applied to the base in the form of a hot melt of the solids of the composition, no or only a very small amount of volatile organic solvent being employed.

Below are given several specific examples illustrating the present invention. The polymerized rosin referred to in certain of these examples had been polymerized with sulfuric acid and had the following characteristics:

Acid number 162 Drop melting point C 109 Color I Example I partial glycerine ester so produced displayed the following characteristics:

Acid number 68 Drop melting point C 124 Color M that use of a lacquer con- Example I! A lacquer was formulated with the partial ester of polymerized rosin prepared in accordance with Example I. as follows:

Parts by Per cent of weight total solids Nitrocellulose g second) 10 45. 5'

Partial ester of xample I.. 8 36. 3

Dibutyl phthalate 4 18. 2

Solvent 78 The solvent employed in this formulation had the following composition:

Percent by weight Butyl acetat I 25 Ethyl aceta 5 Ethyl alcohol 5 Butyl alc ho 15 Toluene Example IV Parts by Per cent of weight total solids Nitrocellulose 04 second) 10 41. 1 Partial ester of Example I 8 33. 3 Paraflin wax (melting point 68 C.) 2 8.3 Dibutyl hthalate. 4 l6. 7 Solvent same as Example II) 76 The lacquer was applied in the form of a thin even film to the surface of a regenerated cellulose sheet. By evaporation, there was obtained a highly moisture-proof regenerated cellulose wrapping material of excellent transparency and brilliancy and which was permanently free from T haze.

Example V Ezample VI Three hundred grams of sulfuric acid polymerized gum rosin having an acid number of 162 and adrop melting point of 109 C. was heated with six grams of glycerine to 270 C. for five hours underan air condenser, CO: being bubbled through the reaction mixture throughout. The product was incorporated in the lacquers of Examples II- to V and employed in the same mannet with the same results. It was noted, however, that if the reaction period was from 1 to 3.5 hours, incomplete combination of the glycerine with the polymerized rosin occurred and the resulting ester imparted an objectionable haze to lacquer and lacquer films prepared therewith. Where 5% of glycerine was employed as in Example I, the use of a reaction period of 3.5 hours or more, for example, 5 hours, resulted in a resin imparting no haze, although a reaction period of less than 3.5 hours, for example, of 1 to 2 hours, resulted in a haze being imparted to the acq er.

From the foregoing, it will be seen that the present invention provides a highly improved resinous material for incorporation in transparent lacquer and the like, provides a process of making suchan improved resinous material, provides an improved lacquer for application to transparent bases, and an improved transparent article coated with such a lacquer, such as transparent regenerated cellulose coated therewith. The present invention enables the convenient and economical use of polymerized rosin in this field'without causing the objectionable development of haze in the film. Numerous other advantages of the present invention will be apparent to those skilled in the art.

A wholly unexpected feature of this invention is that the operable range of acid number is lower when the acid number is reduced by partial esterification with glycerine than when straight polymerized rosin of low acid number is employed.

This application forms a division of my application, Serial No. 372,490, filed December 31, 1940, now Patent No. 2,339,428, of January 18, 1944, entitled "Resin, lacquer containing the same, and article coated with said lacquer.

What I claim and desire to protect by Letters Patent is:

1. A lacquer adapted to yield a moisture-resistant transparent film comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin of acid number of at least about 140 with glycerin, and a volatile organic solvent for said ingredients.

2. A lacquer adapted to be applied to a transparent base and having the property of drying to a transparent, haze-free moisture-proof film comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin of acid number of at least-about 140 with glycerin, a wax, and a volatile organic solvent for said ingredients.

3. A lacquer adapted to be applied to a transparent base and having the property of drying to a transparent haze-free, moisture-proof film comprising from about 25% to about 60% of a cellulose derivative selected from the group consisting of cellulose esters and from about to about 60% of a polymerized rosin ester having an acid number of between about 60 and about 125 obtained .by partial esterification of a polymerized rosin of acid number 01' at least about 140 with glycerin, and a volatile organic solvent for said ingredients, said percentages being by weight and based on the total solids of the lacquer.

4. A lacquer adapted to be applied to a transparent base and having the property of drying to a transparent haze-free, moisture-proof film comprising from about to about'60% of a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, from about 20% to about 80% of a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin of acid number of at least about 140 with glycerin, from about 1% to about 20% or a wax, and a volatile organic solvent for said in redients. said percellulose ethers, r

centages being by weight and based on the total solids of the lacquer.

5. A' lacquer adapted to be applied to a transparent base and having the property of drying to a transparent haze-free, moisture-proof film comprising from about 25% to about of a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, from about 20% to about 60% of a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin of acid number of at least about 140 with glycerin, from about 5% to about 10% of paraffin wax, and a volatile organic solvent for said ingredients, said percentages" being by weight and based on the total solids of the lacquer.

6. A transparent haze-free article of manufacture comprising a transparent base carrying a transparent haze-free film of a composition comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, and a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin oi! acid number of at least about 140 with glycerin.

'7. A transparent haze-free article of manufacture comprising a transparent wrapping sheet carrying a transparent haze-free film of a composition comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, and a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esterification of a polymerized rosin of acid number of at least about 140 with glycerin.

8. A transparent haze-tree article of manufacture comprising a transparent wrapping sheet of regenerated cellulose carrying a transparent haze-free film of a composition comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, and a polymerized rosin ester having an acid number or between about 60 and about obtained by partial esterification of a polymerized rosin of acid number of at least about with glycerin.

9. A transparent haze-free article of manufacture comprising a transparent wrapping sheet of regenerated cellulose carrying a transparent haze-free film of a composition comprising a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers, a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esteriflcation of a polymerized rosin or acid number of at least about 140 with glycerin in a quantity between 2% and 15% by weight or the v,

polymerized rosin, and a wax.

10. A transparent haze-free article of manufacture comprising a transparent wrapping sheet of regenerated cellulose carrying a transparent haze-free film of a composition comprising from about 25% to about 60% of a cellulose derivative selected from the group consisting of cellulose esters and cellulose ethers. from about 20% to about 60% of a polymerized rosin ester having an acid number of between about 60 and about 125 obtained by partial esteritlcation 01' a polymerized rosin or acid number of at least about 140 with glycerin in a quantity between 2% and 5% by weight of thepolymerized rosin, and from about 1% to about 20% of a wax, the said percentages being by weight or the film. AUFRE D L. RBURG. 

